In this randomized clinical trial, we observed no significant benefit to instructions of ad libitum clear liquids up to 2 h versus instructions of standard NPO after midnight in a group of “non-healthy” patients undergoing TAVR or arrhythmia ablation. Previous studies with a shortened fasting protocol, including a large meta-analysis of 5,606 patients (Cheng et al. 2021) demonstrated a significant benefit in subjective assessments of pre-operative well-being, including thirst, mouth dryness and hunger. Of note, most prior studies focused on a healthy patient population, which is consistent with the current ASA fasting guidelines deeming a more liberal protocol safe in “healthy” patients. In addition, the majority of previous studies used a protocol in which beverages, e.g. carbohydrate beverage, were prescribed to patients and included a defined intake volume and composition.

Our study differs from previous studies in several ways. First, patients in our study were allowed more flexibility in the volume and type of beverage consumed. This more pragmatic approach has the benefit of being simple to operationalize and thus potentially translatable to more centers/patients. Second, patients had a significant amount of cardiac dysfunction; 44.8% were previously diagnosed with congestive heart failure, 21% had documented reduced left ventricular ejection fraction on echocardiogram and 26% had known coronary artery disease. It is clinically accepted that patients with significant cardiac co-morbidities have narrower ranges of optimal intravascular volume and it has been posited that an ad libitum protocol might be more flexible and potentially safer for individual patients. Of note, it is unclear to what extent cardiac disease is in and of itself a risk factor for delayed gastric emptying. This is likely to be dependent on the severity of other comorbidities such as diabetes as well as the type and severity of cardiac dysfunction. In heart failure, for example, it has been postulated that several mechanisms may contribute to early satiety, delayed gastric emptying and nausea. These include an imbalance of sympathetic/parasympathetic tone, gut hypoperfusion and bacterial translocation leading to inflammation and volume overload leading to gut edema (Sundaram and Fang 2016). We are aware of only one study that attempted to measure gastric fluid volume in a cardiac surgical population. In this study by Bruer et al. patients undergoing CABG or valve surgery had gastric fluid volumes measured which were approximately normal in each arm (water vs carbohydrate drink vs prolonged fasting) (Breuer et al. 2006).

A potential downside, which may have contributed to our negative results, is that, in practice, many patients might not avail themselves of the opportunity to drink unlimited fluids up to 2 h before surgery due to a variety of factors. Other authors have pointed to examples of large differences in actual fasting times compared to provided fasting instructions, which are potentially explained by poor instructions, unintentional patient non-compliance or other undefined variables (Witt et al. 2021). While there was a significant difference in reported fasting times in our study, i.e. longer fasting time in the control group, the total volume was not recorded as we did not feel this was feasible to accurately record outside of the hospital. However, this may be an important variable. For example, Cheng et al. (Cheng et al. 2021) noted a trend in the literature for better mouth dryness, thirst and hunger scores with an increasing volume of prescribed liquid. Furthermore, the quality of the beverage may be important. In a modular update for 2023 the ASA modified its pre-operative fasting recommendations to specifically encourage consumption of a carbohydrate containing beverage 2 h prior to a procedure. This was based on superiority of the carbohydrate containing beverage versus non-carbohydrate clear liquid or traditional fasting, particularly as it related to pre-operative hunger (Joshi et al. 2023).

While our approach sought to be pragmatic for real world application, a limitation exists in determining the effect of compliance with instructions versus actual fluid intake. Anecdotal experience during our study suggested that some patients did not wish to drink clear liquids up to two hours prior to surgery because of previous instructions to fast after midnight for past surgeries. It is notable that a large percentage, i.e. 64%, of scheduled start times were “first cases”. At our institution first cases begin at 07:30 am, therefore patients would last be able to drink at around 5 am. This coincides with usual sleeping hours for most patients and is a relatively short fasting time, therefore, many patients in the ad libitum up to 2 h before surgery group might not have been thirsty this early in the morning. Nevertheless, an exploratory subgroup analysis of our non-first case patients did not show any difference, though this subgroup analysis is significantly underpowered. Finally, although not formally assessed in our study, many elderly patients have issues with incontinence. Thus, many patients in the more liberal NPO arm of our study may have avoided drinking fluids out of fear of not having easy access to bathroom facilities during their drive to the hospital or while waiting for their surgery. All of the above factors are potential reasons that patients who were randomized to ad libitum liquids up to 2 h prior to surgery may not have availed themselves of this opportunity. This may be important to investigators for future studies as well as to hospitals/clinicians who might consider a more liberal NPO instructions for some of their patients.

None of the secondary end-points were significantly different between the two fasting protocols. Several studies in cardiac surgery (Breuer et al. 2006; Şavluk et al. 2017; Feguri et al. 2019) have shown a trend towards decreased inotrope or vasopressor use in an oral carbohydrate loaded group. In contrast, studies on healthier patients having less invasive surgery have shown no difference (Asakura et al. 2015; Canbay 2017). In our study, a significant proportion of patients received vasopressors intra-operatively, however, there was no difference in this endpoint between the study groups. Potential explanations for this include the fact that patients received significant fluid intra-operatively, on average 1400 ml of crystalloid solution, which may have quickly restored intravascular volume. In addition, the studied procedures are considered minimally invasive as compared to open cardiac surgery and may present less of a surgical insult and concomitant stress response with its associated vasodilation and third spacing.

Comparable hemodynamics and adequate IV fluid administration, in addition to the low predicted incidence of AKI, makes the lack of difference between study arms in post-operative creatinine levels unsurprising. PONV was also similar between groups, which is consistent with previous studies and meta-analyses that did not find a correlation between fasting and pre-operative beverage intake (Cheng et al. 2021).

While our study showed no benefit to a more liberal NPO instruction, an important observation is that there did not appear to be any adverse events. We did not observe any suspected cases of aspiration, nor pre-operative volume overload or heart failure. Given the low incidence of aspiration overall, this study was underpowered to determine safety but may contribute to future analysis in answering this question in an older population with a high burden of co-morbidities. Importantly, we did not observe any case delays in patients randomized to the shorter NPO times. This is significant as case delays can have consequences on operating room efficiency and economics.

Limitations of our study include the unblinded study design and the subjective nature of the patient self-reported satisfaction survey. Also, the predefined vasopressor cut-off is a somewhat arbitrary number although this was modeled off of previous investigations (Tran et al. 2013; Şavluk et al. 2017). Strengths of the study include a randomized design with a relatively large sample size in a well-defined population.

In conclusion, we found that ad libitum clear liquids up to 2 h prior to surgery appeared to be safe with no adverse events or case delays associated with the intervention. No significant differences, however, were observed in our primary or any prespecified secondary endpoints between patients randomized to ad libitum clear liquids up to 2 h prior to TAVR or arrhythmia ablation versus traditional fasting. Based on our results, investigators wishing to study putative benefits of oral fluid loading prior to elective surgery, may consider prescribing, rather than allowing, consumption of fluids 2 h prior to surgery.